The present invention relates to a method of and a system for measuring a stress or a stress distribution, using a stress luminescent material, which method is capable of easily measuring or monitoring a stress value, a stress distribution and a stress image on a measurement object such as a tested body, without physical contacts.
Measuring the magnitude of various kinds of stress occurring in different parts of an object has been considered to be extremely important in every aspect of people""s daily life, especially in the field of designing a machine or a physical facility.
For this reason, there have been developed various different methods for measuring a stress distribution. Among them, a typical and most generally used method requires that an electric resistance strain gauge be attached to an object to carry out a predetermined stress measurement. However, this method only makes it possible to obtain measured data of a portion where a strain gauge has been attached. If it is required to obtain a stress distribution, a great number of strain gauges have to be attached to a great number of measuring points. As a result, a large amount of labour is needed to complete an operation for attaching a great number strain gauges to a great number of measuring points on an object. Moreover, if an object to be measured is relatively small, attachment of strain gauges will be difficult, making it impossible to measure a stress distribution on a small object.
Furthermore, even if a great number of strain gauges are attached to an object which is to be measured, only the measured points can individually give strain data.
On the other hand, in order to make possible the measurement of a stress distribution on a continuous surface, rather than individually measuring many strain points, there has been developed a thermograpy method based on thermoelastic analysis. That is, when a stress is applied on a object, the volume of the object will be changed. This volume change will be accompanied with a temperature change which is called as thermoelastic effect. Thermography is capable of detecting the temperature distribution of an object being measured, so as to measure its stress distribution.
However, the thermograpy not only requires that a periodic stress be added to an object, but also that a synchronism signal of each stress be applied to a camera in order to improve the ratio of S/N (signal/noise). Consequently, it is impossible to perform a stress measurement in a actual operation or a stress measurement in-situ and in real time.
In addition, there has been known another method such as a photoelasticity method in which a transparent resin easy to be measured by an optical means is used to produce a model which is very close to an actual object, a predetermined load is then added to the model so as to measure a stress distribution. However, none of any methods described in the above can be used to easily measure a stress distribution under a condition where the tested body is still being used.
The inventors of the present invention, after having conducted the following experiment, has found the following facts. That is, a stress luminescent powder capable of emitting a light upon receiving a stress is mixed with a transparent optical material to produce a bulk body, alternatively thus obtained mixture is applied to an object so as to form a film thereon. In this way, once the bulk body or the film was used as a test material by applying various loads thereon, it was found that those portions receiving more concentrated stress exhibit a higher luminous intensity, and that such a luminous intensity is proportional to the stress so that it will be increased with an increase in the stress, further that it is possible to visualize a distribution of such a stress by naked eyes. Moreover, upon repeating the experiment under various different conditions and after repeating related studies, it was clearly understood that there is a correlation between the luminous intensity and a stress.
The tested body may be formed by a bulk body prepared by mixing a powder of the stress luminescent material with a transparent material, or a film obtained by at first mixing the powder of the stress luminescent material with the transparent material and then applying the mixed materials to the surface of a measurement object. However, the above-mentioned correlation can be used in both of the two cases, i.e., with one case using the bulk body as a tested body, and the other case using the above film to form a tested body, thereby obtaining similar effects.
The present invention has been accomplished in accordance with the above newly found knowledge, and its object is to solve the problems existing in the above-described conventional stress measuring methods. Namely, it is an object of the present invention to provide a method and a system which, by making use of a stress luminescent material, renders it possible to directly observe a stress distribution on the base of a real time without using a cord, and to easily measure a stress or a stress distribution and a stress image.
In order to solve the above problems, a method for measuring a stress distribution using a stress luminescent material is characterized in that said method comprises the steps of application of a stress to a tested body containing a stress luminescent material whose light emission is proportional to the stress, making visually observable a stress distribution over the tested body in accordance with a luminous intensity of the stress luminescent material contained in the tested body.
Furthermore, the method of the present invention is characterized in that said method comprises the steps of adding a stress to a tested body containing a stress luminescent material whose light emission is proportional to the stress, comparing a detected value of the luminous intensity of the stress luminescent material contained in the tested body with certain correlation data indicating a relationship between the luminous intensity of the stress luminescent material and a stress, thereby obtaining a stress value or a stress distribution over the tested body.
The tested body used in the measuring method of the present invention may be suitably formed by a bulk body prepared by mixing a powder of the stress luminescent material with a transparent material, or is formed using a film obtained by at first mixing the powder of the stress luminescent material with the transparent material and then applying the mixed materials to the surface of a measurement object, or the tested body is formed using a film obtained by at first mixing the powder of the stress luminescent material with an organic binder and then applying the mixed materials to the surface of the measurement object.
The luminous intensity of the stress luminescent material of the tested body may be effectively detected by using a peak value of an emission spectrum obtained through a spectroscope. Alternatively, it is effective that the luminous intensity of the stress luminescent material is detected while at the same time illuminating the tested body using an illumination light having a wave length which is different from the peak value of the emission spectrum. Of course, this can also be done by adding a filter in front of the photodetector, the filter of which can only pass the light with the wavelength of the stress luminescent material.
Moreover, a system for measuring a stress or a stress distribution using a stress luminescent material of the present invention is characterized in that said system comprises a tested body containing a stress luminescent material whose light emission is proportional to the stress; a photodetector for detecting the luminous intensity of the stress luminescent material of the tested body; computing means capable of comparing a detected value from the photodetector with certain correlation data indicating a relationship between the luminous intensity of the stress luminescent material and a stress, and then computing a stress over the tested body; a display device capable of displaying the tested body""s received stress which has been computed by the computing means.
In this measuring system, an optical path such as a glass fiber may be connected between the tested body and the photodetector. Further, it is also possible that a spectrometer for detecting the peak value of an emission spectrum of the stress luminescent material may be connected between the tested body and the photodetector.
Furthermore, a system for measuring a stress image using a stress luminescent material of the present invention is allowed to include a tested body containing a stress luminescent material whose light emission is proportional to the stress; photographing means capable of taking a two-dimensional image of the luminous intensity of the luminescent material contained in the tested body; and a display device capable of displaying as a stress image by the photographed luminous intensity.
With the use of the above measuring method, the luminous intensity of the tested body containing the stress luminescent material is proportional to a compression stress, a tensile stress and a shearing stress so that it will increase with an increase in any of these stresses. Accordingly, it is possible to visualize a stress distribution over the tested body in accordance with a luminous intensity of the stress luminescent material contained in the tested body.
Furthermore, the correlation data indicating a relationship between a luminous intensity and a stress may be prepared in advance by way of experiment. Then, if a stress is applied to the tested body and the luminous intensity at a specific point of the tested body is measured, and if the measured value is compared with the correlation data indicating a relationship between a stress and the luminous intensity of the above stress luminescent material, it is possible to know the stress value on the specific point of the tested body since a stress corresponding to the detected luminous intensity may be made known.
Then, if the measuring point is moved and stress values on different positions of a tested body are obtained, it is possible to quantitatively know a stress distribution over the tested body.
The measurement of a stress or a stress distribution over a tested body may be carried out by a measurement system including a photodetector for detecting the luminous intensity of the stress luminescent material of the tested body; a computing means capable of comparing a detected value from the photodetector with certain correlation data indicating a relationship between the luminous intensity of the stress luminescent material and a stress, and then computing a stress on the tested body; a display device capable of displaying the tested body""s received stress which has been computed by the computing means. Therefore, it is possible to efficiently and correctly measure and record the stress or the stress distribution over the tested body.
Furthermore, the luminous intensity of the stress luminescent material of the tested body may be detected only by using a peak value of an emission spectrum obtained through a spectrometer. Alternatively, the luminous intensity of the stress luminescent material may be detected while at the same time illuminating the tested body using an illumination light having a wavelength which is different from the peak value of the emission spectrum. In this way, it is possible to remove an undesired influence from the surrounding lights and to improve a measurement precision. Of course, this can also be done by adding a filter in front of the photodetector, the filter of which can only pass the light with the wavelength of the stress luminescent material.
In addition, since the luminous intensity of each point on the tested body will change corresponding to a received stress, if a two-dimensional luminescent image is photographed, it is possible to obtain a stress image indicating a two-dimensional stress distribution and its change with time.